The primary objective of pork production is to produce lean meat in a cost effective and sustainable manner. From a nutritional perspective, energy is perhaps the most critical nutrient, because it is the most expensive to provide in the diet. Other nutrients are less expensive to provide, and can always be provided in amounts that meet or exceed the pig’s requirement for growth. Because energy is considered the most important driver of growth in the diet, achieving the full genetic potential for growth in the modern pig requires a clear and definitive understanding of the energy response curve in all phases of production. Establishing responses to nutrient intake levels is particularly critical in defining feeding programs to optimize carcass quality.
Two experiments were therefore conducted by the Prairie Swine Centre to develop energy response curves for pigs during the growing and finishing phases of production. The first experiment was conducted at the Centre. Each room contained 20 pens, with 5 pigs per pen, or 300 pigs on test. This experiment employed 5 experimental treatments in each of three phases of growth. Diets varied from 3.00 to 3.60 Mcal/kg DE. The increase in diet DE concentration was achieved by increasing canola oil, wheat and soybean meal at the expense of barley.
Energy density of the diet did not affect pig growth, bodyweight, or the variability in growth during any growth phase (P>0.05). Feed intake decreased as energy density of the diet increased (P<0.001); consequently, feed efficiency improved (P<0.001). However, because of the increased cost of the high energy rations, feed costs per pig increased by 20% as diet DE increased from 3.0 to 3.6 Mcal/kg (Figure 1). Back fat thickness increased from 16.8 to 19.4 mm as diet DE increased from 3.0 to 3.6 Mcal/kg (P<0.001). Carcass value, and premiums paid, however, were surprisingly not different among energy levels (P>0.10). Therefore, the increased cost of the high energy diets made them uneconomical to feed.
Upon reviewing the results of experiment #1, we wondered if the level of feed intake impacted the response to energy. Feed intake, which typically varies a lot amongst farms, could conceivably mitigate a response to the higher energy diets. Therefore, a commercial farm was considered as another model to evaluate the response of pigs to dietary energy concentration.
The second experiment was conducted at St. Denis Stock Farm, located at St. Denis, SK, about 50 km east of Saskatoon, SK. It is a single site, 600-sow farrow-to-finish operation constructed about 10 years ago. It operates as a strictly commercial entity, and is not normally used for research. Three grower and 3 finisher rooms, with 12 pens each were utilized. Each pen housed 20 pigs, for a total of 36 pens and 720 pigs on test.
Three dietary energy levels were employed: 3.20, 3.35 and 3.50 Mcal DE/kg. This range in energy was selected as it represented the reasonable expected range of energy used in typical commercial diets in western Canada. Ingredient and nutrient composition are shown in Table 1. This table shows the formulated and the actual DE, which was determined for each treatment and gender at the mid-point of each phase. The deviation we observed between formulated DE values and determined DE values in the experimental diets confirms the importance of this measurement. The average deviation between formulated and determined DE, reported herein, was 71 kcal/kg, or 2.1%, a significant amount in the context of practical swine diet formulation.
The diets were formulated according to commercial practice, such that increasing the energy content of the diet resulted in increased use of wheat, soybean meal and tallow, and less barley. The upper limit of tallow levels in the highest energy diets – 4.0% – was determined by the handling capacity of most on-farm mills, especially during the winter months.
Pigs performed very well on this experiment, with daily gain averaging 990 g/d across treatment. Average daily gain and feed efficiency were improved during the early phases of the experiment (P<0.05). Up to about 80 kg, there was no effect of diet on average daily feed (P>0.10), so increased dietary energy concentration resulted in increased daily energy intake (P<0.05). However, beyond about 80 kg, pigs tended to consume less of the higher energy diets, so growth rate was not affected by diet during this period. Of particular interest to commercial barn operators was the observation that the number of tail-end pigs, those that did not achieve the target shipping weight within the room turn period, was higher on the lower energy diet (Table 2). Interestingly, dietary energy did not affect carcass backfat thickness, lean yield, carcass index or carcass value (P>0.10). However, the higher energy diets tended to increase loin thickness (P<0.10), something we have seen in previous experiments. The dressing percentage of the pigs on the low energy diet tended to be lower than pigs on the other treatments (P<0.10). The dietary energy concentration did not improve the uniformity of the pigs, nor the uniformity of their carcasses. Thus, producers should not increase diet energy concentration with the expectation that pigs will reach market in a more uniform manner, or produce more uniform carcasses. The latter will be much more dependent on selection practices at the time of shipping. An economic analysis was conducted using longer-term average prices for pigs (1.45/kg) and ingredients: (wheat, $130/t; barley, $110/t; soybean meal, $340/t; canola meal, $204/t, tallow, $550/t) (Table 3). Two possible scenarios for the adoption of these results on a commercial farm were considered. In scenario #1, all pigs were shipped by the time the finishing room was turned over to the next group; some pigs would be marketed below the core weight and revenues reflected the associated lost value. Under this circumstance, the best return over growout feed cost was earned on the lowest energy diet, with an advantage in the range of $2.12 compared to the medium energy program, and $4.04 over the high energy program. In the second scenario, the tail-end pigs were held back until they reached the minimum market weight; this resulted in a higher gross income, since all pigs would be marketed within the optimum weight range, but the cost would be higher, since there would a considerable increase in the feed required. Space to house the tail-end pigs would also be required. In this scenario, the advantage again fell to the lowest energy program, earning $1.26 more than the medium energy program, and $4.02 compared to the high energy program. In the latter scenario, no charge for housing was included, as it was assumed that hold-back pigs would be moved into an existing hold-back room, or would be placed with other pigs. In conclusion, net income can be maximized by feeding lower energy programs. However, the results of individual phases within this experiment suggest that feeding higher energy diets up to 80 kg may be warranted, as this is the period when pigs would respond the most to the higher energy diets. It is clear from this experiment, and from others conducted previously, that the response to dietary energy concentration is not easy to predict. If pigs are able to consume sufficient quantities of feed to achieve excellent growth on lower energy diets, then feeding higher energy diets is unlikely to be beneficial. However, if feed intake is low, then there may be a benefit to feeding higher energy diets, to increase daily energy intake and thus support faster growth. Nonetheless, we caution producers from assuming that increasing dietary energy will universally increase pig performance; experimental data does not support such an assumption. Finally, in terms of gross numbers, the numerical difference in growth rate between the low and higher energy diets was very similar at St. Denis as compared to the Prairie Swine Centre; while conducting research at multiple locations is obviously preferable, it is also very expensive. These comparative data confirm the validity of the response of pigs housed under the conditions of the Prairie Swine Centre.